Re: [PHP-DEV] some notes about traits
On 16 November 2011 00:17, Rasmus Schultz ras...@mindplay.dk wrote:
Here's a better example of something useful that actually works:
trait Accessors
{
public function __get($name)
{
return $this-{'get'.$name}();
}
public function __set($name, $value)
{
$this-{'set'.$name}($value);
}
}
class OrderLine
{
use Accessors;
public $price;
public $amount;
public function getTotal()
{
return $this-price * $this-amount;
}
}
$line = new OrderLine;
$line-price = 20;
$line-amount = 3;
echo Total cost: .$line-total;
I like that example. It shows, at a fairly simple level, the ability
to compose a class from potentially multiple traits.
Putting the __magic_methods in a trait, what a great idea. This
mechanism is allows for all sorts of easy to expand ideas.
You _COULD_ use this trait to implement discrete getters and setters ...
?php
/**
* Trait to provide setter and getter functionality
* with an exception for any missing method.
*/
trait Accessors
{
public function __get($name)
{
if (method_exists($this, 'get' . $name))
{
return $this-{'get' . $name}();
}
elseif (property_exists($this, $name))
{
return $this-{$name};
}
else
{
throw new Exception(Cannot retrieve value of
'$name'.);
}
}
public function __set($name, $value)
{
if (method_exists($this, 'set' . $name))
{
$this-{'set' . $name}($value);
}
elseif (property_exists($this, $name))
{
$this-{$name} = $value;
}
else
{
throw new Exception(Cannot set value for '$name'.);
}
}
}
/**
* @property float $price
* @property float $amount
* @property float $tax
* @property-readonly float $total
*/
class OrderLine
{
use Accessors;
protected $price;
protected $amount;
protected $tax;
public function getTotal()
{
return $this-price * $this-amount * (1 + ($this-tax / 100));
}
protected function getPrice()
{
return $this-price;
}
protected function getAmount()
{
return $this-amount;
}
protected function setPrice($price)
{
$this-price = $price;
}
protected function setAmount($amount)
{
$this-amount = $amount;
}
}
$line = new OrderLine;
$line-price = 20;
$line-amount = 3;
$line-tax = 10;
echo Total cost: .$line-total;
?
outputs ...
Total cost : 66
So, the actual methods are hidden from public, but a developer can
extend the class to add additional processing.
Interestingly, I've used property_exists to expose public access to
protected properties. I suppose that is always possible. Bad design
really. I would guess you wouldn't mix the different access mechanisms
(public/protected/private, __get/__set, getter()/setter()).
Richard.
--
Richard Quadling
Twitter : EE : Zend : PHPDoc : Fantasy Shopper
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Re: [PHP-DEV] some notes about traits
Hi Rasmus: On 16 Nov 2011, at 01:17, Rasmus Schultz wrote: I knew about the traits features in Scala, and I guess I assumed this would be similar - not so. Right, they are not the same. PHP's traits are much closer to the notion of traits introduced in the Smalltalk world, while Scala's traits are rather like mixins as for instance in Ruby. Aside issues like typing and whether that type information is preserved, the main difference is that PHP's traits do not use implicit conflict resolution. I believe the key to understanding traits, is understanding that traits are in fact an implementation detail - an artifact that does not really change or affect the nature of OOP in PHP as such, and by design, should not. I understand that now - thank you :-) From my perspective, a key difference from classes and interfaces, is that traits have no meaningful use at run-time - no type-hinting and with no real reflection-features that reveal the details. They cannot implement interfaces for classes, but classes can use them to implement interfaces. Traits just provide a set of method implementations that can be aggregated by classes. So in a sense, they're a design-time tool for the programmer. I like that explanation, thanks! So I guess my remaining quibble is that the documentation needs to relay this somehow - with a basic real-world example that actually uses an interface too, to clarify the difference, and to demonstrate how this tool use useful in conjunction with class and interface declarations. Hello world really doesn't explain anything, other than the syntax. [...] This may be a little too magical for an example in the documentation though - and doesn't demonstrate interfaces. I'll ponder this and post a better example if I can think of one... :-) As someone else already pointed out, there are tools to contribute such nuggets to the documentation. Please submit a patch. And just one other comment: var_dump($test instanceof CartBehavior); // = false Why would it be beneficial to throw an exception here? CartBehavior is a trait, and not a class or interface. The instanceof operator has no meaning for traits - it always returns false. You could argue that false is the expected result - I would argue that the only reason this happens to work at all, is because traits internally are classes. Suppose you thought you were actually doing a meaningful type-check of some sort? If by mistake you put a trait-name where you meant to put the name of an interface or class, such an error could be very hard to spot. While I agree that it can be hard to spot, I would usually advocate for less intrusive alternatives. Hmmm, well, I could put in a warning in strict mode, I guess. But that would require a consistent handling within all the other APIs we got, too. Especially is_a is such a candidate. And changing is_a seems to be a non-trivial thing. So, I will need to look carefully at that. Would be great if you could file a bug report for that. I hope this feedback is useful :-) Yes it is. I think it is especially important that other people actually write down their understanding of the mechanism. Blog posts, mailing list posts, improved documentation, they are all important. Thanks Stefan -- Stefan Marr Software Languages Lab Vrije Universiteit Brussel Pleinlaan 2 / B-1050 Brussels / Belgium http://soft.vub.ac.be/~smarr Phone: +32 2 629 2974 Fax: +32 2 629 3525 -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] some notes about traits
who can hook me up with a login, so I can contribute to the documentation? Here's a better example of something useful that actually works: Assuming your example is OK, you could edit the doc and submit it as a patch at https://edit.php.net.
Re: [PHP-DEV] some notes about traits
On 11/16/11 6:12 PM, Rasmus Schultz wrote: who can hook me up with a login, so I can contribute to the documentation? You can do it as an anonymous user on edit.php.net. Join in the chat so you can prod someone to merge your changes - you might also need to remind the doc mail list. Once you've had a few patches committed you will likely get karma to commit directly. Chris Here's a better example of something useful that actually works: Assuming your example is OK, you could edit the doc and submit it as a patch at https://edit.php.net. -- Email: christopher.jo...@oracle.com Tel: +1 650 506 8630 Blog: http://blogs.oracle.com/opal/ -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] some notes about traits
Hi Stefan,
Appreciate you taking the time to discuss this - and I apologize if I
jumped the gun with some of these comments.
I knew about the traits features in Scala, and I guess I assumed this would
be similar - not so.
Reading through my own remarks and your comments, I now have a better
understanding of what traits are, and how they're intended to be used.
I believe the key to understanding traits, is understanding that traits are
in fact an implementation detail - an artifact that does not really change
or affect the nature of OOP in PHP as such, and by design, should not. I
understand that now - thank you :-)
From my perspective, a key difference from classes and interfaces, is that
traits have no meaningful use at run-time - no type-hinting and with no
real reflection-features that reveal the details. They cannot implement
interfaces for classes, but classes can use them to implement interfaces.
Traits just provide a set of method implementations that can be aggregated
by classes. So in a sense, they're a design-time tool for the programmer.
So I guess my remaining quibble is that the documentation needs to relay
this somehow - with a basic real-world example that actually uses an
interface too, to clarify the difference, and to demonstrate how this tool
use useful in conjunction with class and interface declarations. Hello
world really doesn't explain anything, other than the syntax.
Here's a better example of something useful that actually works:
trait Accessors
{
public function __get($name)
{
return $this-{'get'.$name}();
}
public function __set($name, $value)
{
$this-{'set'.$name}($value);
}
}
class OrderLine
{
use Accessors;
public $price;
public $amount;
public function getTotal()
{
return $this-price * $this-amount;
}
}
$line = new OrderLine;
$line-price = 20;
$line-amount = 3;
echo Total cost: .$line-total;
This may be a little too magical for an example in the documentation though
- and doesn't demonstrate interfaces.
I'll ponder this and post a better example if I can think of one... :-)
And just one other comment:
var_dump($test instanceof CartBehavior); // = false
Why would it be beneficial to throw an exception here?
CartBehavior is a trait, and not a class or interface. The instanceof
operator has no meaning for traits - it always returns false.
You could argue that false is the expected result - I would argue that the
only reason this happens to work at all, is because traits internally are
classes.
Suppose you thought you were actually doing a meaningful type-check of some
sort? If by mistake you put a trait-name where you meant to put the name of
an interface or class, such an error could be very hard to spot.
Since there is no such thing as an instance of a trait, the instanceof
operator should not work for traits.
Once again, thank you for taking the time to talk about this, Stefan - I
hope this feedback is useful :-)
- Rasmus
On Fri, Nov 11, 2011 at 12:02 PM, Stefan Marr p...@stefan-marr.de wrote:
Hi Rasmus:
First, sorry, I don't have currently the time to reiterate all discussions
on these questions.
Please, do me the favor and search the archives for previous discussions.
I believe _all_ points you raise here have been discussed and commented
before, and most of them quite recently.
Since I believe the answers are already given,
let me try another approach to tackle your problems.
From my perspective the purpose of traits is often misunderstood.
So, let me ask a few questions. They might sound basic,
but I want to better understand your design rational,
and the reasons behind your implementation approach.
If you got the time, please try to answer all of them.
They might seem suggestive, or even worse, 'rhetorical',
but that is not on purpose.
Answering them will help us all better to understand
what the underlying issues/conceptual problems are we need to tackle,
either by improving the current implementation and/or documentation.
On 11 Nov 2011, at 17:00, Rasmus Schultz wrote:
class Cart
{
public static $instance;
# public function addItem(CartBehavior $item, $amount=1) // = script
terminates
public function addItem($item, $amount=1)
{
echo Adding {$amount} {$item-getName()} to shopping cart - price =
.($amount * $item-getPrice()).\n\n;
}
}
What is the real purpose of adding the type hint for CartBehavior here?
My understanding would be, you want to express/document that the given
object is required to support a specific set of operations.
Is there any other semantics that need to be expressed by this annotation?
On a practical level, you probably want to make sure that the engine never
barks at you because it got an object that does not understand a certain
operation.
Is it relevant for the method using that object that it provides a
specific implementation for the required set of
Re: [PHP-DEV] some notes about traits
On 11/15/11 4:17 PM, Rasmus Schultz wrote: So I guess my remaining quibble is that the documentation needs to relay this somehow - with a basic real-world example that actually uses an interface too, to clarify the difference, and to demonstrate how this tool use useful in conjunction with class and interface declarations. Hello world really doesn't explain anything, other than the syntax. Here's a better example of something useful that actually works: Assuming your example is OK, you could edit the doc and submit it as a patch at https://edit.php.net. Chris -- Email: christopher.jo...@oracle.com Tel: +1 650 506 8630 Blog: http://blogs.oracle.com/opal/ -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] some notes about traits
Hi Rasmus:
First, sorry, I don't have currently the time to reiterate all discussions on
these questions.
Please, do me the favor and search the archives for previous discussions.
I believe _all_ points you raise here have been discussed and commented before,
and most of them quite recently.
Since I believe the answers are already given,
let me try another approach to tackle your problems.
From my perspective the purpose of traits is often misunderstood.
So, let me ask a few questions. They might sound basic,
but I want to better understand your design rational,
and the reasons behind your implementation approach.
If you got the time, please try to answer all of them.
They might seem suggestive, or even worse, 'rhetorical',
but that is not on purpose.
Answering them will help us all better to understand
what the underlying issues/conceptual problems are we need to tackle,
either by improving the current implementation and/or documentation.
On 11 Nov 2011, at 17:00, Rasmus Schultz wrote:
class Cart
{
public static $instance;
# public function addItem(CartBehavior $item, $amount=1) // = script
terminates
public function addItem($item, $amount=1)
{
echo Adding {$amount} {$item-getName()} to shopping cart - price =
.($amount * $item-getPrice()).\n\n;
}
}
What is the real purpose of adding the type hint for CartBehavior here?
My understanding would be, you want to express/document that the given object
is required to support a specific set of operations.
Is there any other semantics that need to be expressed by this annotation?
On a practical level, you probably want to make sure that the engine never
barks at you because it got an object that does not understand a certain
operation.
Is it relevant for the method using that object that it provides a specific
implementation for the required set of operations?
[Side note for the archive: traits do not guarantee that]
var_dump($test instanceof CartBehavior); // = false
Beside testing the corner cases of the language definition,
is there any practical need for this test?
Do you have an example where it is desirable to know exactly
that a particular implementation is provided by an object?
var_dump((new ReflectionClass('Product'))-getTraits()); // CartBehavior is
a ReflectionClass?
Well, the reflection API is not perfect yet. Other interesting features,
like knowing how conflicts where resolved are missing, too. (I think)
The reason for that is unfortunately missing time.
Secondly, the instanceof operator doesn't complain when you test to see if
an object carries a trait - if this isn't going to work, it should at least
throw an exception.
You refer to the previous example, I suppose:
var_dump($test instanceof CartBehavior); // = false
Why would it be beneficial to throw an exception here?
$test is not an instance of CartBehavior, since traits cannot be
instantiated, and do not provide any guarantees in what ever respect.
So, even if a class uses CartBehavior, you would never be sure that
it actually also uses all of the implementations provided by it.
Lastly, when you reflect on a trait, it comes back as an instance of
ReflectionClass. As pointed out, traits are probably more similar to
interfaces than they are to classes, and they definitely don't have
properties, as are exposed by the ReflectionClass type.
[Well, it can be useful to test for the properties expected by a trait.]
Yes, that is an implementation artifact of how the reflection API is designed.
I would also point out that the examples in the documentation (which it
seems were just copied from the RFC?) do not demonstrate any real purpose
of this feature. Is this the most anybody has attempted to do with this
feature? Trying to come up with a real example, I didn't get very far
before running into these stumbling blocks.
I frequently search for usages of traits on the web, and by now, there are
quite a number
of articles giving examples and discussing the pros and cons of traits.
So, no, you are not the first one.
But, yes, the current documentation page could use some better examples.
If I can't use instanceof to check for a trait (A), then I would at least
expect to be able to write a trait that implements an interface (B) - does
that not seem reasonable or logical?
The discussion we had on that topic evolved to the following proposal:
https://wiki.php.net/rfc/horizontalreuse#requiring_composing_class_to_implement_interface
However, to my understanding, there was no consent on actually adding this.
Having to use both the interface and the trait as a pair, and having to
explicitly apply them both to the class, feels like a work-around.
The discussions we had here suggest otherwise: this is exactly the way to go
from a conceptual perspective.
It keeps the two concepts apart, avoids confusion, and thus, is the conceptual
purer alternative.
However, by answering my questions from above, you can certainly make a point
